As is well known to those skilled in the related arts, one of the primary components of a cathode ray tube (CRT) display apparatus is the electron gun or guns. In particular, a visual display is created on a phosphorescent screen by a CRT by scanning one or more electron beams across the screen to selectively illuminate picture elements (pixels) on the screen to create a desired display pattern. A monochrome CRT typically comprises a single electron gun. A color CRT typically comprises three electron guns (corresponding to the colors red, green and blue). The combination of the three primary colors in different ratios on any given pixel can create any color in the visible spectrum.
Typically CRTs are manufactured in a clean room environment. Even the slightest contamination by dust or other particles in the neck assembly (which houses the electron gun and the space through which the electron beam or beams travel from the gun to the screen) may significantly affect operation of the CRT. Particularly, if a dust particle or other particle is struck by an electron beam, it typically would cause the CRT to arc, resulting in a current surge in the CRT. The particular lead or leads on which the current surge would occur depends on a number of factors, such as the particular electron beam which struck the particle. The surge, however, would most likely occur on the focus leads and/or ground leads of an electron gun. If the current surge is great enough, it can burn out one or more of the electronic components of the CRT.
Even if an arcing event does not destroy or harm electronic components, it can cause the calibration of the electron gun or guns to be changed. For instance, in a color monitor, the three electron guns are calibrated relative to each other to create the desired color scheme. If these guns are calibrated while a dust particle is in the electron path of one of the guns, they will be calibrated to certain values relative to each other. If a dust particle which existed in the electron path when the initial calibrations were made is later zapped (burned by the electron beam), the initial calibrations may no longer be valid. For instance, if the red electron gun was adjusted to a nominal voltage of 40.2 volts in order to create the desired color scheme, and a dust particle in its electron beam path is later zapped, the 40.2 volts adjustment may no longer be valid and the display may become skewed toward the red end of the color spectrum.
Arcing in the field, leading to operational failure of the CRT or at least to color skew, is one of the more common field failure mechanisms in CRTs.
Most CRT manufactures have quality assurance tests which test the CRT for many possible defects including the existence of particles in the electron beam path which cause or may cause arcing or excessive arcing. It is known that as the number of arcing events increases during manufacturing and/or testing, the more likely the CRT unit is to continue arcing in the field. Excessive arcing during testing indicates that the CRT was either manufactured under less than perfectly clean conditions or that its hardware is itself defective. In either event, it suggests that arcing will continue to occur in the field.
If the arcing was due to dust, as opposed to hardware defects, arcing is likely to continue to occur because it is possible and even likely that other dust particles exist in the neck assembly and that they will move during transportation, thus not causing arcing during testing, but only after the unit is sold and in operation in the field.
Accordingly, it is desirable to determine how often a CRT arcs during the manufacturing and/or quality assurance testing of the unit. Although during manufacturing and testing, a CRT unit may be powered up and operating for several hours (during which time arcing may occur), most of this time is spent outside of the presence of a person who can actually observe the occurrence of arcing. For instance, during manufacturing, a CRT is typically "burned" in an aging tunnel for at least an hour. In the burning process, a CRT unit is powered up and operated in a high temperature environment in order to stabilize its components, particularly the aperture grill. The aperture grill affects the alignment of the beams and typically does not stabilize until at least thirty to forty-five minutes of operation in an aging tunnel. The burning stage is normally conducted outside of the observation of humans.
Accordingly, it is an object of the present invention to provide a method and apparatus for detecting and counting arcing events of a CRT.
It is another object of the present invention to provide a low power, low cost, and digital method and apparatus for detecting arcing in a CRT.
It is a further object of the present invention to provide an improved CRT arc detector.